Assuming that Samsung really has recently sold 40 million Galaxy S4s, and assuming that it did hit 20m in early July, we can estimate that the time it took for Samsung to make the jump from 20 to 40 million sales was roughly 114 days, which is two weeks faster than the figure we calculated for the S3.

All these numbers should be taken with a pinch of salt, as it's hard to know precisely when particular milestones were met, and Samsung's numbers generally represent sales to retailers, rather than sales to actual individuals. That said, it appears that the Galaxy S4 may be selling at roughly the same pace as last year's S3.

Whether Samsung's happy with that is tough to know. It's definitely a lot of phones to flog, but I suspect the South Korean tech giant will have been hoping for sales that significantly outpace last year's edition.